The present invention relates to image forming apparatuses that can handle recording sheets of non-fixed form (hereinafter, also referred to as non-standard) sizes.
In an image forming apparatus which forms images such as toner images on recording sheets, in the case of a fixed form (hereinafter, also referred to as standard) size recording sheet, for the size information related to the length and breadth of a recording sheet, generally the size information detected automatically in the sheet feeding tray (hereinafter, referred to merely as a tray) on which recording sheets are stacked is used.
Further, such type of trays have sensors placed at positions at which it is possible to detect the sizes of fixed form size recording sheets, and the information of these sensors is output to the main unit side of the image forming apparatus. Therefore, the size of the recording sheet is not being detected accurately but is one that discriminates between different fixed form sizes based on the rough detection result.
Further, it is also possible to use non-fixed form size recording sheets other than fixed form size sheets.
Therefore, there are even image forming apparatuses that have trays for loading non-fixed form size recording sheets, and when non-fixed form size recording sheets are loaded, it is possible to set that the tray is a non-fixed form size tray.
Further, if there is any error in the input or setting of the size of the recording sheet when using non-fixed form size recording sheets in this manner, this can cause problems such as jamming at the time of feeding or conveying the sheets.
In view of this, methods have proposed as set forth in Patent Document 1 through Patent Document 3 shown below when such non-fixed form size recording sheets are loaded in the tray.
[Patent Document 1]                Tokkai 2000-125083 (Japanese Non-Examined Patent Publication)        
[Patent Document 2]                Tokkaihei 6-23942 (Japanese Non-Examined Patent Publication)        
[Patent Document 3]                Tokkaihei 11-79472 (Japanese Non-Examined Patent Publication)        
In Patent Document 1 above, the user measures beforehand the size of the recording sheet and sets in the main unit of the apparatus the recording sheet size data for each tray (numerical input). Next, when sheets are loaded in the tray for which the selection has been made that the tray is a non-fixed form size tray, the size data set for each tray in the main unit of the apparatus is referred to at the time of sheet feeding.
Further, in Patent Document 2 mentioned above, the transfer sheet is placed first on the platen and scanned thereby measuring the size of the sheet. In this case, it is necessary that the apparatus is a copying machine provided with a scanner, and also, this requires the tedious tasks of placing the recording sheet on the platen and of scanning it.
Further, in Patent Document 3 mentioned above, the size of the recording sheet is measured by passing the transfer sheet through the image forming apparatus without forming images on it. In this case, a new sensor will become necessary to measure the size accurately in the main scanning direction, and it is necessary to output a blank recording sheet.
In this manner, it is possible to obtain the size of a non-fixed form size recording sheet using the techniques given in Patent Documents 1 to 3 mentioned above. However, the setting of the size of a non-fixed form size recording sheet in an image forming apparatus is normally done for each tray. Therefore, for example, when wanting to use non-fixed form size recording sheets of the same size in all the plurality of trays provided in the image forming apparatus, in spite of different problems such as the above being present, it is necessary to obtain the size of the non-fixed form size recording sheets several times. In addition, for example, after setting the size of a non-fixed form size recording sheet for a certain tray, if recording sheets of a size different from the set size are used in that tray, and even in the case when again non-fixed form size sheets of the size set previously are to be used, in spite of different problems such as the above being present, it is necessary to obtain the size of the non-fixed form size recording sheets.
Further, although it is possible to solve this problem by placing sensors that can accurately measure the size of even non-standard sheets in the tray, there will be problems that arise such as the increase in the cost due to the addition of sensors to the trays or of adopting sensors that can measure accurately, or the increase in cost for taking measures in the main unit of the image forming apparatus to receive the data from the trays.